1. Field of the Invention
The present invention relates to a shoulder arthroplasty system to surgical reconstitution of the human or animal shoulder and, in particular, to a humerus implant.
2. Description of Relevant Art
The shoulder joint is a ball-and-socket joint, which has an exceptional range of motion. Shoulder instability and other maladies of the shoulder joint, such as arthrosis, may require a replacement of the joint.
A shoulder joint prosthesis, which includes the replacement of the convex head of the humerus, is disclosed in U.S. Pat. No. 7,819,923. It reflects the orientation and the center of rotation of actual joints. In the case of a worn or damaged rotator cuff or too much bone loss, such prosthesis would not recover the range of motion. In such a case, a reverse shoulder prosthesis may be preferable. An example of such prosthesis is disclosed in the U.S. Patent Application Publication No. 2009/0210065 A1. In such prosthesis, the humeral component includes a stem and a cup attached to the stem. The glenoid component supports a convex head, which articulates with the cup of the humeral component.
U.S. Pat. No. 7,445,638 B2 discloses an implant with the stem and a removable basket shaped support. This support is seated in the cavity of a humerus head and fixedly connected to the stem. A load bearing polyethylene insert is connected to a stem by a cylindrical shaft, which was inserted into a hole of the shaft, further fixing the removable basket shaped support to the stem.
An implant as disclosed in the US Patent Application Publication No. 2009/0306782 A1 requires only a minimum of bone material to be removed. Here fixation of the implant within the bone is far less stable compared to a stem.
An improved stemless implant is disclosed in the US Patent Application Publication No. 2012/0179263 A1 by the same inventors of this application. The implant has a cup shaped body with an outer thread. The thread has a plurality of fins with cutouts between the fins. The fins have inclined leading surfaces to minimize insertion torque.